1. Field of the Invention
The invention relates to data storage with respect to data storage systems, and more particularly to a system for dynamic reuse of logical data objects.
2. Background Information
Traditionally, operating a write once read many (WORM) media relies on media type itself, so that a single physical data object cannot be both a standard read-write data object and a WORM enforced data object. These two media types are made mutually exclusive at manufacturing time. While it would be advantageous to have a common pool of physical media used for both WORM and read-write data object, it has not been physically possible based on the attributes bound to the media at manufacturing time. One WORM attribute required of WORM media is a 12 byte World Wide Identifier (WWID) that is unique per each media cartridge created. The WWID is used by software to tie written content on the media to a world unique instance of that media independent of any potential labeling changes of the data object. This allows software to detect anomalies or malicious behavior that may result in one data object being mistaken for another different physical media instance.
In the context of computer systems, the term “volume” is often used to describe a single accessible data storage area with a single file system that is resident on a media, such as a tape of a tape drive. As discussed herein, the terms “data object”, “logical object”, “logical data object”, and “object” are used to refer to a volume, such as a tape volume or virtual tape volume. As is known in the art, the term volume is used interchangeably with “tape volume”, “virtual tape volume”, tape VOLSER (Volume Serial number), tape file volume, file volume, and file system.
A logical WORM environment has the same requirement for the WWID. The logical data objects may be inserted/created in a virtual library using an emulated media type. Software must know the independent media pools to direct appropriate input and/or output to the intended media pool. It would be advantageous if the virtual library could manage one common media pool and not need separate media pools for standard read-write and logical WORM data objects. Also, different logical WORM media data objects with the same data object serial number must be detectable. For physical tape media, each tape cartridge has the WWID generated and embedded into the cartridge at the time of manufacture independent of its data object serial number or VOLSER. Application software honoring WORM media may use the WWID in order to detect when the physical media has been replaced, thus detecting potential malicious behavior. In a virtual storage system, a physical media object may not be directly associated with a virtual object. Instead, the virtual object may be a simple file stored in a disk subsystem. The file then has meta-data associated with it that can be stored in a database independent of the file. The chain of custody patterns of the file may complicate things since the virtual object may be replicated and/or offloaded to multiple physical data objects. The overall lifecycle of the virtual object may introduce numerous events where its contents may be compromised.
For example, an independent server may write the same data object serial number that may be stacked to a physical cartridge. If that physical cartridge were to be relabeled and inserted falsely into the original server, its contents, including the stacked logical data object, may not be detected as different or having changed.
Occasionally, a data object is mistakenly returned to a common pool in a ‘scratch’ state. A data object, either WORM or read-write, in a scratch state indicates that any data on the data object as expired, or is invalid, and can be deleted, or overwritten, and the data object reused as a new data object. For WORM data, this represents a data loss condition that is particularly undesirable. If such a mistake occurs, a previously written WORM data object could be overwritten with non-WORM type data or different WORM data.